Combined effects of vortex flow and the Shchelkin spiral dimensions on characteristics of deflagration-to-detonation transition

The objective of this investigation was to achieve the shortest possible distance for the deflagration-to-detonation transition (DDT) for a pulse detonation engine without losing the engine’s simplicity. The effects of rapid flame propagation, rotating velocity, and Shchelkin spiral dimensions in the vortex flow (VF) on DDT characteristics were examined. A VF field was established in the ignition and transition domains of a detonation tube using a VF-type injector. The flame propagation in the ignition domain was observed by a high-speed video camera and the detonation propagation process was observed by measuring the pressure and ionization current in the detonation tube. The DDT distance in the VF could be shortened by 50–57 % of that in the counterflow by optimizing the VF and the Shchelkin spiral dimensions. The shortening effect became remarkable as the rotating velocity increased. The governing factors for this effect are considered to be the formation of an area of higher energy density in the ignition domain of the tube, as well as flame acceleration due to rapid flame propagation in the VF and turbulence promotion near the tube wall by the rotating velocity and the Shchelkin spiral in the transition domain of the tube. However, the combined effects of VF and the Shchelkin spiral on the shortening of the DDT distance were deteriorated in very strong turbulence. It is necessary to optimize the rotating velocity and dimensions of the Shchelkin spiral to achieve the shortest possible distance of DDT in the VF.     

Host–Guest Hydrogen Bonding Varies the Charge‐State Behavior of Magnetic Sponges

The electron‐donor(D) and ‐acceptor(A)‐assembled D₂A‐layer framework [{Ru₂(m‐FPhCO₂)₄}₂TCNQ(OMe)₂]?nDCE ( 1‐nDCE ; m‐FPhCO₂^?=m‐fluorobenzoate; TCNQ(OMe)₂=2,5‐dimethoxyl‐7,7,8,8‐tetracyanoquinodimethane; DCE=1,2‐dichloroethane) undergoes drastic charge‐ordered state variations via three distinct states that are a two‐electron‐transferred state (2e‐I), a charge‐disproportionated state (1.5e‐I), and a one‐electron‐transferred state (1e‐I), depending on the degree of solvation by nDCE. The pristine form 1‐4DCE has a paramagnetic 2e‐I state, which eventually produces the solvent‐free form 1 in 1.5e‐I via an intermediate state 1‐nDCE (n≤1) in 1e‐I. Resolvation of 1 stabilizes 1‐DCE , allowing it to switch between 1.5e‐I and 1e‐I, and to become ferrimagnetic with a T_c of 30 K (1.5e‐I) and 88 K (1e‐I). The stabilization of the 1e‐I state of 1‐DCE is due to the presence of host–guest hydrogen bonding that enables to suppress the electron‐donation ability of D even in an identical framework with 1 .     

Dynamics and mechanism of iodine sorption by polyacetylene

Sorption of iodine by bulk polyacetylene was studied under various I₂ gas pressures at 25°C. The sorption dynamics show that the penetration of iodine into PA is not Fickian and the diffusion coefficient increases with time of sorption. A discontinuous increase in the sorption isotherm is observed at P/P₀ = 0.25 (P is the pressure of the I₂ gas and P₀ is the saturation value at 25°C). It is due to iodine penetration into PA crystals, as evidenced by x-ray analysis. The distribution of iodine within crystals is apparently inhomogeneous: some unit cells are changed into “iodine-PA” cells, while others remain unchanged. The electrical conductivity depends not only on the amount of iodine but also on the I₂ gas pressure under which sorption is carried out. At given iodine content, the conductivity of a sample doped under higher I₂ pressure is greater than that of a sample doped under lower pressure.     

Analysis of anomalous X-ray diffraction effects of isotactic polystyrene gels and its implications for chain conformation and isomeric homogeneity

Oriented gels, obtained by high supercoolings of isotactic polystyrene solutions, exhibit unexpected “fiber-type” x-ray diffraction patterns. In particular a pronounced meridional reflection at a spacing of 0.51 nm, together with its successive orders, requires an extended, or nearly extended, chain conformation which appears irreconcilable with the stereochemistry of isotactic polystyrene. Furthermore, the value of 0.51 nm correlates directly with the axial projected repeat expected for two styrene monomer units. Two possible stereosequences merit atention: syndiotactic and syncephalic (head-to-head, tail-to-tail). In addition to the 0.51 nm meridional reflection, layer lines are observed with spacing 3.06 nm (6 × 0.51) which equate with 24 carbon–carbon bonds in the backbone. Cylindrically averaged Fourier transform calculations for the various models are compared with the observed x-ray results and the best fit is obtained for a 24/11 helix of isolactic polystyrene with the syncephalic stereosequence. This conclusion, however, clashes with the ¹³CNMR evidence which indicates that the polymer is essentially isotactic. The implications of these novel results in relation to gel crystallization are discussed.     

Disorientation of crystallites in highly stretched polyethylene

Crystallite orientation in polyethylene has been investigated in the high range of stretching. Crystallite disorientation can be observed in samples subjected to various stretching procedures: hot drawing and elongation of oriented fibers at room temperature at constant rate and at constant load. Crystallite disorientation does not take place during elongation but is induced upon removal of the applied stress. The higher the rate of removal of stress the greater is the disorientation. Two mechanisms are postulated for the disorientation: one relating to the irregular residual strain developed in fibrils by high stretching, and the other concerning rotational movement of crystallites caused by amorphous chains terminated on the interfaces. The fibrillation brought about by high stretching is thought to play an important role in the crystallite disorientation.     

Hydrogen production by photosynthetic microorganisms

Applied Biochemistry and Biotechnology - Hydrogen is a clean energy alternative to the fossil fuels, the main source of greenhouse gas emissions. We developed a stable system for the conversion of...     

Lithiation of 5,6-dihydrouridine: a new route to 5-substituted uridines

2',3'-$\text{O}$-Isopropylidene-5'-$\text{O}$-methoxymethyl-5,6-dihydrouridine ($\text{2}$) was found to serve as an “amide α-anion” upon lithiation with LDA. Reactions of the anion with acid chlorides followed by phenylselenation and oxidative elimination furnished 5-acyluridines. For the preparation of 5-alkyluridines, initial introduction of phenylselenenyl group at the C-5 of $\text{2}$ appeared to be effective. Alkylation of its α-selenenyl carbanion and subsequent generation of 5,6-double bond produced 5-alkyluridines. These routes constitute a new entry to 5-substituted uridines.     

Carrier doping effect into quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron-correlation by Cu(II) ions, [Ni1-xCux(chxn)2Br]Br2-x

This communication will describe the electron doping effect into Ni(III) complexes by Cu(II) ions, [Ni(1-x)Cu(x)(chxn)(2)Br]Br(2-x) (x = 0.038 and 0.101) by using an electrochemical oxidation method. A drastic increase of electrical conductivity as well as a new absorption band around 0.5 eV in single crystal reflectance spectra was observed by doping Cu(II) ions, indicating the electron doping was successfully made. An ESR result shows unpaired electrons locate in the d(x2-y2) orbitals of Cu(II) and have almost no interaction with those of other ions.